This invention relates to an exhaust emission control apparatus for a Diesel engine, and more particularly to an apparatus of the kind above described which can regenerate a filter provided for collecting particulates contained in engine exhaust gases.
As means for minimizing emission of particulates contained in exhaust gases of a Diesel engine, an apparatus is known in which a filter is disposed in the exhaust pipe to collect the particulates, and a burner is provided for burning the collected particulates thereby reducing the pressure loss across the filter due to the presence of the collected particulates.
However, since the filter is usually made of a porous ceramic material capable of withstanding a high temperature of about 1,200.degree. C. to 1,300.degree. C., while, on the other hand, the combustion temperature of the particulates is about 500.degree. C. to 600.degree. C., the filter will be damaged by the heat generated from the burner when the heat of combustion exceeds 1,300.degree. C. although the combustion of the particulates may be successfully attained.
In order to avoid damage to the filter due to the heat, it is necessary to control the fuel supply so that the combustion temperature of the particulates in the filter is maintained within the range of from 600.degree. C. to 1,200.degree. C., and the particulates only can be efficiently burnt. As means for controlling the fuel supply, a fuel control system including an air assist type burner as disclosed in Japanese patent application Laid-open No. 57-212317 (1982) has been proposed and has achieved a considerable success in practical use. However, proposed auto emission standard have set forth a target of a very high level in regard to the amount of particulates contained in exhaust gases of Diesel engines. Therefore, in order to achieve the target of the very high level set forth by the these standards the prior art fuel control system including the an air assist type burner, and using assist air at a predetermined pressure to control the pressure of fuel continuously supplied for combustion of particulates, has had limitations from the viewpoint of more accurate electronic control of the amount of fuel supply and also from the viewpoint of satisfactory atomization of fuel.